The present invention pertains to Integrated Services for Digital Networks (ISDN) and more particularly to trunk circuitry for interfacing between an ISDN system and T-carrier facilities.
In general, an Integrated Services Digital Network is a system which provides end to end digital connectivity to a wide variety of services by users having multi purpose user network interfaces. ISDN systems provide voice switching, packet data switching, signalling networking and wideband networking capabilities.
ISDN systems typically provide for data transmission and reception employing a particular format. Usually, this format is incompatible with T-carrier data formats. The data transmission rates of ISDN systems and T-carrier facilities are typically in the megabit per second range. Conversion of data from the ISDN format to the T-carrier format and vice versa must be done rapidly. In addition, circuitry must operate both for receiving and transmitting data simultaneously.
Further, due to the flexibilities of the ISDN system, large strings of logic 0 data is produced. In contrast, T-carrier facilities cannot tolerate more than 15 consecutive logic zeroes in a string of transmitted data bits. Therefore, interfaces between T-carrier facilities and ISDN systems require high-speed conversion of strings of zero data into non-zero data strings and high-speed recovery of the zero data strings at the distant end of the T-carrier facility.
Therefore, it is an object of the present invention to provide a high-speed receiver/transmitter interface between T-carrier facilities and an ISDN system.
It is another object of the present invention to provide a high-speed zero data bit conversion and recovery arrangement.